1. Field of the Invention
The present invention relates to a communication control method, a radio base station, and a radio control station.
2. Description of the Related Art
The Third-Generation Partnership Project (3GPP) and the Third-Generation Partnership Project 2 (3GPP2), both of which are formed by regional standardization organizations and other members, have been involved in standardization of the third generation mobile communication methods or so-called IMT-2000. The 3GPP defines standard specifications concerning the W-CDMA method while 3GPP2 defines standard specifications concerning the cdma2000 method.
Based on a forecast that high-speed and large-volume traffics attributable to download from databases or Web sites will be increased particularly in downlinks along rapid diffusion of the Internet in recent years, the 3GPP defines specifications of “High Speed Downlink Packet Access (HSDPA)” which is a high-speed packet transmission method for downlink communication (see 3GPP TS25.308 v5.7.0, for example). Meanwhile, from the same point of view, the 3GPP2 defines specifications of the “1xEV-DO” which is a transmission method specially designed for high-speed downlink data in downlink communication (see 3GPP2 C. S0024 Rev. 1.0.0, for example). Here, in the cdma2000 1xEV-DO, the term “DO” stands for “data only”.
In a Release 99 system according to the W-CDMA method, one-to-one communication channels called dedicated physical channels are provided between a radio base station and mobile stations, and communications are achieved by use of these dedicated physical channels. In this case, power resources, code resources and other resources to be consumed will be increased along with an increase in the number of mobile stations communicating with the radio base station.
In addition to the dedicated physical channels to be provided one-on-one between the radio base station and the mobile stations, a shared physical channel to allow a plurality of mobile stations to share one large channel is provided in a Release 5 system according to the W-CDMA method. The communication method using the shared physical channel is called High Speed Downlink Packet Access (HSDPA), which is the high-speed packet transmission method capable of transmitting high-speed and large-volume traffics. In the HSDPA method, a plurality of mobile stations shares a single shared physical channel, and a radio base station makes the base station scheduling (Node-B scheduling) of transmissions of packets to the plurality of the mobile stations by selecting one mobile station which uses the shared physical channel, at each time transmission intervals (which is referred to as TTI and is equal to 2 ms in the HSDPA). In this way, HSDPA achieves improvement in radio resource use efficiency. Moreover, HSDPA achieves reduction in transmission delays, higher use efficiency of radio resources, and higher transmission rates by using techniques including the Medium Access Control-HSDPA (MAC-hs) retransmission control and adaptive modulation encoding at radio sections between the radio base station and the mobile stations.
Both of the Release 99 system and the Release 5 system (HSDPA) according to the W-CDMA method are a radio access method for performing transmission while multiplying transmission signals by spreading codes, and it is possible that data from different users are multiplexed among codes and are transmitted at the same time and in the same radio frequency band in these systems. Thus, data transmitted through the dedicated physical channel and data transmitted through the shared physical channel are multiplexed among codes and are transmitted at the same time and in the same radio frequency band. Accordingly, it is possible to operate the two lines of communication in the same radio frequency band. In other words, the Release 5 system according to the W-CDMA method is a system in which both communication using the dedicated physical channel and communication using the shared physical channel are simultaneously used in the same radio frequency band.
In the system in which both communication using the dedicated physical channel and communication using the shared physical channel are simultaneously used in the same radio frequency band, the radio resources including the power resources and the code resources are shared by the dedicated physical channel and the shared physical channel.